1. Field of the Invention
The present invention relates to a method of driving a plasma display panel in accordance with a matrix display scheme.
2. Description of Related Art
At present, as thin display devices, AC (alternate current discharge) type plasma display panels are commercially available on the market. Since such plasma display panels utilize the discharge phenomenon to emit light, discharge cells only have two states, i.e., a xe2x80x9clight emissionxe2x80x9d state corresponding to the highest luminance level and a xe2x80x9cnon-light emissionxe2x80x9d state corresponding to the lowest luminance level. Thus, a subfield method is employed to implement gradation driving for providing halftone display luminance levels corresponding to an input video signal. The subfield method involves constituting one field display period by N subfields in correspondence to each bit digit of N-bit pixel data corresponding to an input video signal. Then, a number of light emissions (light emitting period) is allocated to each of the N subfields corresponding to a weighting factor applied to each bit digit of the pixel data to selectively emit light in respective discharge cells in accordance with the pixel data bits.
For example, when one field display period is constituted by six subfields SF1-SF6 as shown in FIG. 1, each of the subfields is allocated the following number of light emissions:
SF1: 1
SF2: 2
SF3: 4
SF4: 8
SF5: 16
SF6: 32
In this case, when discharge cells are driven to emit light only in SF6 of the subfields SF1-SF6, light is emitted 32 times through one field display period, so that a display luminance at luminance level xe2x80x9c32xe2x80x9d is viewed. On the other hand, when discharge cells are driven to emit light in the subfields SF1-SF5 except for the subfield SF6, light is emitted a total of 31 times (16+8+4+2+1) through one field display period, so that a display luminance at luminance level xe2x80x9c31xe2x80x9d is viewed.
Stated another way, combinations of subfields in which discharge cells are driven to emit light enables a so-called 64-level gradation luminance display, in which 64 luminance levels can be provided in a stepwise manner.
Here, as shown in FIG. 1, a light emission driving pattern within one field period for driving a discharge cell to emit light at luminance level xe2x80x9c32xe2x80x9d is reverse to that for driving a discharge cell to emit light at luminance level xe2x80x9c31.xe2x80x9d In other words, during one field period, a discharge cell which should be driven to emit light at luminance level xe2x80x9c31xe2x80x9d is in a non-light emitting state in a period in which a discharge cell which should be driven to emit light at luminance level xe2x80x9c32xe2x80x9d is emitting light, and the discharge cell which should be driven to emit light at luminance level xe2x80x9c32xe2x80x9d is in the non-light emitting state in a period in which a discharge cell which should be driven to emit light at luminance level xe2x80x9c31xe2x80x9d is emitting light. In this event, if the screen displays an image that includes a region in which a discharge cell which should be driven to emit light at luminance level xe2x80x9c32xe2x80x9d (hereinafter referred to as the xe2x80x9cdisplay region E32xe2x80x9d) and a discharge cell which should be driven to emit light at luminance level xe2x80x9c31xe2x80x9d (hereinafter referred to as the xe2x80x9cdisplay region E31xe2x80x9d) are located adjacent to each other, a trouble will arise as follows.
For example, when the line of sight is moved from the display region E32 to E31 immediately before a discharge cell existing in the display region E32 transitions from a non-light emitting state to a light emitting state, the non-light emitting state of both discharge cells are viewed in succession. As a result, a dark line is viewed on the boundary of both discharge cells. This dark line appears on the screen as a spurious border which is not at all related to any pixel data, thus resulting in a degraded display quality.
In addition, since the plasma display panel utilizes the discharge phenomena to implement the gradation driving based on the subfield method, this involves initialization of all discharge cells, setting of discharge cells to be driven for emitting light, and soon, as well as the light emission operation as described above. Therefore, the plasma display panel must conduct discharges not related to the contents of an image, giving rise to a problem that the contrast is degraded in the image by the light emission resulting from such discharges.
Further, a general consideration in commercializing such PDP at present is to realize lower power consumption.
The present invention has been made to solve the problem mentioned above, and its object is to provide a plasma display panel driving method which is capable of improving the contrast with low power consumption while suppressing spurious borders.
A plasma display panel driving method according to the present invention drives a plasma display panel to display in gradation representation in accordance with a video signal. The plasma display panel has discharge cells, functioning as pixels, at intersections of a plurality of row electrodes corresponding to display lines with a plurality of column electrodes arranged to intersect the row electrodes. The method comprises the steps of selectively producing a writing discharge only in discharge cells except for discharge cells serving to display a luminance level xe2x80x9c0xe2x80x9d only in a first subfield of a plurality of subfields constituting one field display period in the video signal to initialize the discharge cells to a light emitting cell state; selectively producing an erasure discharge in the discharge cells remaining in the light emitting cell state in accordance with pixel data corresponding to the video signal only in one of the remaining subfields except for the first subfield to have the discharge cells transition to a non-light emitting cell state; and driving only the discharge cells in the light emitting cell state to emit light in each of the subfields the number of light emissions allocated thereto corresponding to a weighting factor applied to each of the subfields.